Kelly and Kornienko had circled the Earth 5,440 times and travelled 143 million miles during the 340days they spent in space.

Their ground-breaking long visit to the International Space Station, the longest for any American, was designed to test human reactions to being in space for prolonged periods in preparation for a manned mission to Mars in coming years.

Kelly was also part of an experiment comparing his development and changes in space with his identical twin brother -- Mark -- back on Earth.

Kelly captured imaginations worldwide by posting stunning views of Earth from space on his Instagram page and tweeting regularly to nearly a million followers.

Russia continues hold the world record for duration in space of 438 days.